Western Rattlesnake

Contents:
 
Links:
Taxon, Status, and Ranks Habitat Photos
General Description State Status Comments
Identification Tips Inventory & Research Needs Key Features
Phenology Threats & Mgmt Concerns
Range References Distribution Map

Taxon, Status, and Rank

Species Crotalus viridis     (Rafinesque, 1818)
  = Crotalus oreganus (Holbrook, 1840)
Family Viperidae
(Pit Vipers)
Status none
State Rank S5
Global Rank G5

Caution: This is a venomous and potentially dangerous snake. Rattlesnakes rarely strike unless harassed, handled or stepped on, but any encounter within the striking range could result in a bite.

General Description

This is a heavy-bodied snake with large dark spots, a wide triangular head, a distinct eye stripe, and a rattle at the tip of the tail. The largest rattlesnake measured in the Northwest was 150 cm (59 in.). Most adult snakes encountered in Washington are much smaller (around 2 ft. or 60 cm). The cryptic coloration of these snakes varies depending on habitat and substrate color. Typically it is some shade of brown or olive. The spots are dark brown and bordered by black and then white. Additional spotting occurs on the sides of the body. The dorsal spots fuse with the lateral spots on the tail to form bands. Ventral scales are white with dark blotches. The dorsal scales are strongly keeled and overlapping with 25 rows (range 23-29) at mid-body. The pupils are vertical and the scale above the eye is enlarged. Holes, called “pits,” for reception of infrared heat are located on both sides of the face near the nostrils. Rattlesnakes bear live young. Recently born snakes (neonates) resemble adults but have more vivid coloration and the rattle is limited to a single, silent, horny segment called a “button.” An additional button is added with each shedding. No obvious external features distinguish males from females. See Photos Page.

Identification Tips

The Western Rattlesnake is the only snake in Washington with a rattle and facial pits.

The Gopher Snake (Pituophis catenifer) is often misidentified as a rattlesnake because the two species have similar markings and defensive behavior. Gopher Snakes differ in their physical appearance by lacking a rattle and facial pits. They also have smaller, square, dorsal spots; oval pupils; a narrow eye stripe that extends both to the posterior edge of the jaw and below the eye; and scales that are less keeled.

Night Snakes (Hypsiglena torquata) resemble juvenile rattlesnakes but differ in lacking a rattle and facial pits. They also have smaller, more numerous dorsal spots that are not outlined in black and white, a pearly white belly with no other markings and smooth scales. See Key Features Page.

Phenology

In most of the Columbia Basin, rattlesnakes emerge from their overwintering sites (hibernacula or dens) in April. Activity is limited to the vicinity of the overwintering site for 2-3 weeks and then they disperse to their summer foraging areas. Reproduction takes place in the spring near the den site. Young start to appear in late August. Adults return to the overwintering sites starting in late September, although activity may continue until late October depending on location and temperatures.

Range

Rattlesnakes occur east of the Cascade Mountains in the East Cascades, Columbia Basin, Okanogan and Blue Mountain ecoregions. The furthest west they have been documented is in the Columbia Gorge approximately 1 mile west of Dog Mountain in Skamania County. See Distribution Map.

For information on the complete range of this species, see NatureServe Explorer.

Habitat and Habits

In our state, Western Rattlesnakes primarily occur in shrub-steppe habitats but are also found in Oregon white oak, ponderosa pine and other open forest types. Talus and basalt rock outcroppings are used for overwintering.

Rattlesnakes are active during the day when temperatures are moderate but switch to nocturnal activity during the hottest months of the year. When not active, they shelter under shrubs and rocks.

State Status Comments

This species is common and widespread in eastern Washington but numbers in many areas have declined because of habitat loss, excessive hunting at den sites and destruction of den sites.

Inventory and Research Needs

Observations from areas not indicated on the map can be submitted to the WDFW herp database by contacting Lori Salzer by E-mail salzeljs@dfw.wa.gov. Of particular interest are observations that occur outside the known distribution.

Current or Recent Research in Washington

Radio-telemetry studies by WA DNR Natural Heritage Program (Lisa Hallock) in Grant County and WA Department of Fish and Wildlife in Okanogan County (Scott Fitkin) were conducted in 2003 and 2004 to locate communal hibernacula.

Threats and Management Concerns

The main conservation concern for this species is excessive hunting and wanton killing of snakes emerging from hibernation, as well as destruction of communal den sites. Both can result in local population declines and even local extirpation.

References

Ashton & Queiroz (2001), Klauber (1956), Hallock (1998, 2004), Pook et al. (2000), Prior and Weatherhead (1996)

Personal communications: Scott Fitkin




Hallock, L.A. and McAllister, K.R. 2005. Western Rattlesnake. Washington Herp Atlas. http://www1.dnr.wa.gov/nhp/refdesk/herp/

Last updated: December 2005


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